. Insomnia is a common complaint in elderly subjects. There is general agreement that optimal management of the problem should be directed at the underlying cause. But currently there is no universally agreed on approach, so that elderly with this complaint are commonly simply treated with sedatives/hypnotic medications. This application is based on the belief that a conceptual framework is needed to tackle insomnia that is based on physiology. It is hypothesized that age-related changes in sleep/circadian systems in the elderly are the core of the problem. Such changes can produce insomnia on their own and augment the effect of sleep disorders that interrupt sleep (apnea or myoclonus) or somatic disorders (pain, chronic cough, etc.). This provides a testable set of hypotheses that have important treatment implications. These concepts lead to a case-control study of insomnia which is ideally suited to the proposed multi-factorial origins of the complaint. In this study, major streams of investigation in this area will be united, an epidemiological approach, based on self-report of symptoms and physiological study of age-related changes in sleep in small numbers of subjects, often with no complaints of insomnia. In our study we will identify controls as those with no or rare trouble sleeping in the previous one year, while cases will have current, frequent trouble sleeping that is at least of three weeks duration. The status of case-controls will be confirmed by objective testing so that cases and controls can be analyzed with only subjective definitions or with both subjective and objective definitions. Individuals with depression will be excluded by a careful two-stage screening process since depression is a risk factor for insomnia and insomnia is a risk factor for depression. This complex interaction will confound our analysis. Measures include: sleep characteristics, the 24 hour temperature and melatonin rhythms and the response to sleep deprivation. The plans will specifically address the following questions: 1) what is the relative role of phase advance of the biologic clock, low melatonin levels and decreased sleep process(s) in the genesis of insomnia?; 2) are sleep apnea and nocturnal myoclonus risk factors for insomnia in the elderly?; and 3) do age-related changes in the sleep/circadian system augment the effect of sleep apnea, nocturnal myoclonus, and somatic disorders that can interrupt sleep in terms of the risk of insomnia? The approach is aimed at the development of a new diagnostic framework for insomnia and new treatment approaches.